This invention relates to light dimming systems, and, more particularly, to an apparatus for simultaneously controlling the brightness of a plurality of discrete indicator lamps.
In aircraft, it is desirable to simultaneously control the brightness of the various annunciator or indicator light-emitting devices, such as incandescent lamps or light-emitting diodes, of the various aircraft instruments, from maximum brightness to completely off, to match the light level of the surrounding environment. Thus, during bright daylight conditions, these indicating lights operate at maximum brightness to insure that they will be readily observed when lit; conversely, under very dark, overcast, night-time conditions, it is desirable that these indicating lights be operated at a very low degree of illumination.
Generally, aircraft instruments are energized by connecting these instruments across a constant direct voltage, generally +28 volts to ground. In many self-contained aircraft instruments, in which various control leads and power leads are brought out to terminal boards or connection plugs, one side of each indicating lamp included in such self-contained instruments is connected to an individual ground line which is brought out to a terminal board or plug, and the other side of the indicating lamp is internally connected through a switching device to a constant voltage dc power line, to which other circuit elements are also internally connected, with only the one constant voltage power line being brought out to the terminal board or plug for connection to an external power supply line. Thus, a light dimming system for simultaneously controlling light intensities of a plurality of indicating lights connected between an energized line and ground, in which only the ground sides of indicating lights are accessible for connection to the dimming system, is highly desirable for use in aircraft.